Hydrazide derivatives of polyamides and their medical use as chelating agents

ABSTRACT

The invention relates to certain substituted derivatives of aminopolycarboxylic acids and metal chelates thereof. The compounds are particularly suitable for use as diagnostic agent. For example, the compounds can be used as radiodiagnostic agents, detoxification agents and contrast agents for diagnostic imaging processes. In particular, the high relaxivity paramagnetic metal chelates of substituted aminopolycarboxylic acids are especially suited for use as magnetic resonance imaging contrast agents.

This application is a 371 of PCT/EP 92/01598 F.D. Jul. 16, 1992.

The present invention relates to certain novel polyamine chelatingagents, in particular to hydroxamate and hydrazide derivatives ofpolyamines, and to their uses, especially their medical uses.

The medical use of chelating agents is well established, for example asstabilizers for pharmaceutical preparations, as antidotes for poisonousheavy metal species and as diagnostic agents for the administration ofmetal species (e.g. ions or atoms) for diagnostic techniques such asX-ray, magnetic resonance imaging (MRI) or ultrasound imaging orscintigraphy.

Polyamine chelating agents, for example aminopoly(carboxylic acid orcarboxylic acid derivative) (hereinafter APCA) chelating agents andtheir metal chelates, are well known and are described for example inU.S.A.-2407645 (Bersworth), U.S.A.-2387735 (Bersworth), EP-A-71564(Schering), EP-A-130934 (Schering), EP-A-165728 (Nycomed AS),DE-A-2918842 (Rexolin Chemicals AB), DE-A-3401052 (Schering),EP-A-258616 (Salutar), DE-A-3633245 (Schering), EP-A-263059 (Schering),EP-A-277088 (Schering) and DE-A-3633243 (IDF).

Thus, for example, EP-A-71564 describes paramagnetic metal chelates, forwhich the chelating agents are nitrilotriacetic acid (NTA),N,N,N',N'-ethylenediaminetetraacetic acid (EDTA),N-hydroxyethyl-N,N',N'-ethylenediaminetriacetic acid (HEDTA),N,N,N',N",N"-diethylenetriaminepentaacetic acid (DTPA) andN-hydroxyethylimino-diacetic acid, as being suitable as contrast agentsfor MRI, contrast being achieved by the effect of the magnetic field ofthe paramagnetic species (e.g. Gd(III)) with the chelating agentsserving to reduce the toxicity and to assist administration of thatparamagnetic species. Amongst the particular metal chelates disclosed byEP-A-71564 was GdDTPA, the use of which as an MRI contrast agent hasrecently received much attention. The Gd(III) chelate of1,4,7,10-tetraazacyclododecanetetraacetic acid (DOTA), referred to inDE-A-3401052 (Schering) and in U.S.A.-4639365 (Sherry/University ofTexas), has also recently received attention in this regard.

More recently, a number of modifications to the basic APCA structureshave been proposed to provide chelating agents with improved stability,water solubility, selectivity or toxicity. This includes for exampleproviding hydrophilic substituents as described by Nycomed inEP-A-299795 or altering the structure of bridging chains between theamine nitrogens as described by Schering in EP-A-250358.

In the field of hepatobiliary MRI contrast agents, where lipophilicityis desired, Nycomed (in EP-A-165728) have proposed the use ofparamagnetic chelates of certain anilide group-containing iminodiaceticacids and Lauffer in WO-A-86/06605 has suggested the use of paramagneticchelates of triaza and tetraaza macrocycles which carry a fused aromaticring but are otherwise unsubstituted.

However, all hitherto known APCA chelating agents and their metalchelates encounter problems of toxicity, stability, selectivity orsuppressed relaxivity and there is thus a general and continuing needfor such polyamine chelating agents which form metal chelates of reducedtoxicity or improved stability, water solubility, selectivity orrelaxivity.

We have now found that certain substituted derivatives ofaminopolycarboxylic acids and metal chelates thereof are particularlysuitable for use as diagnostic and therapeutic agents, for example asradiotherapeutic agents, as detoxification agents and as contrast agentsfor diagnostic imaging processes. In particular we have found that highrelaxivity paramagnetic metal chelates of such substituted APCAderivatives are especially suited for use as MRI contrast agents.

In one aspect the present invention therefore provides a compound offormula I

    A X(CR.sup.1 R.sup.2).sub.n !.sub.m XA                     (I)

or a chelate complex or salt thereof, for use as therapeutic ordiagnostic agent

wherein in formula I,

each of the groups R¹ and R² may independently represent a hydrogen atomor an alkyl or alkoxy group, optionally carrying one or moresubstituents selected from hydroxy, alkoxy and aryl groups;

each X independently represents an oxygen or sulphur atom or,preferably, a group NA;

each A independently represents a hydrogen atom or an alkyl groupoptionally substituted by a group Y;

each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R⁶, CSZ, PO₂ Zor B;

or one or more pairs of A groups on different X moieties may togetherform a group (CR¹ R²)_(n) X¹ !_(p) (CR¹ R²)_(n) or a group A on amid-chain nitrogen may represent a group (CR¹ R²)_(n) X¹ !_(p) (CR¹R²)_(n) X¹ A where p represents an integer of 0 to 6, preferably 0, andeach X¹ independently represents an oxygen or sulphur atom or a groupNA¹ where A¹ is as defined for A but may not form part of a groupattached to more than one nitrogen atom;

or two adjacent groups R¹ and/or A may together form a homo- orheterocyclic saturated or unsaturated 5-7 membered ring containing 0, 1or 2 ring heteroatoms selected from oxygen, nitrogen and sulphur;

each group B represents a group CONR⁷ (OR⁸), CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂,SO₂ R⁷, SO₂ NR⁷ R⁸ or NO₂ ;

each group Z independently represents a group OR⁶, SR⁶ or NR⁶ ₂ ;

each of the groups R⁶ independently represents a hydrogen atom, or analkyl group optionally substituted by one or more hydroxy, alkoxy oraryl groups;

each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups or a lipophilic group M, preferably incorporating or linked via ahydrolysable (e.g. ester) linkage;

m is an integer of 2 to 8, preferably 2, 3 or 4;

n is an integer of 2 to 4, preferably 2 or 3, especially 2;

with the provisos that where the compound of formula I is linear andeach X is NA and two terminal A groups carry Y groups of formulaCON(OR⁸)R⁷, then in said terminal A groups (i) if R⁸ is hydrogen R⁷ isother than hydrogen or C₁₋₃ alkyl (preferably other than unsubstitutedalkyl) and (ii) if R⁷ is alkoxylated alkyl R⁸ is other than methyl(preferably other than unsubstituted alkyl), that at least two,preferably at least three non-B ionisable Y groups are present, that atleast one Y group represents a non-ionisable group B, and preferablythat if each X is a group NA and each group A is Y-containing(especially where m is 2 and each A is a group --CH₂ Y) and two groups Acontain B groups then if these B groups are CONHNR₂ ⁸ one or more R⁸group is other than methyl (preferably other than unsubstituted C₁₋₃alkyl).

In a further aspect the present invention also provides a compound offormula Ic

    A X(CH.sub.2).sub.2 !.sub.3 XA                             (Ic)

or a chelate complex or salt thereof

(wherein in formula Ic,

each X represents a group NA;

each A independently represents a hydrogen atom or an alkyl groupoptionally substituted by a group Y,

or the two terminal A groups together form a group (CH₂)₂ X¹ !(CH₂)₂where X¹ represents a group NA¹ where A¹ is as defined for A but may notform part of a group attached to more than one nitrogen atom;

each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R⁶, CSZ, PO₂ Zor B;

each group B represents a group CONR⁷ (OR⁸), CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂,SO₂ R⁷, SO₂ NR⁷ R⁸ or NO₂ ;

each group Z independently represents a group OR⁶, SR⁶ or NR⁶ ₂ ;

each of the groups R⁶ independently represents a hydrogen atom, or analkyl group optionally substituted by one or more hydroxy, alkoxy oraryl groups;

each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups or a lipophilic group M, preferably incorporating or linked via ahydrolysable (e.g. ester) linkage;

with the provisos that where the compound of formula I is linear and twoterminal A groups carry Y groups of formula CON(OR⁸)R⁷, then in saidterminal A groups (i) if R⁸ is hydrogen R⁷ is other than hydrogen orC₁₋₃ alkyl (preferably other than unsubstituted alkyl) and (ii) if R⁷ isalkoxylated alkyl R⁸ is other than methyl (preferably other thanunsubstituted alkyl), that at least two, preferably at least three non-Bionisable Y groups are present, that at least one Y group represents anon-ionisable group B, and preferably that if each X is a group NA andeach group A is Y-containing (especially where each A is a group --CH₂Y) and two groups A contain B groups then if these B groups are CONHNR₂⁸ one or more R⁸ group is other than methyl (preferably other thanunsubstituted C₁₋₃ alkyl).

In formulae I and Ic, ionisable groups Y are preferably carboxyl orcarboxylate groups and alkyl and alkylene moieties in groups A, A¹, R¹,R², R⁶, R⁷ and R⁸ may be saturated or unsaturated (but preferablysaturated) straight-chained or branched and preferably contain from 1 to8, especially preferably 1 to 6, and most preferably 1 to 3, carbonatoms. Alkyl moieties in Y-substituted A and A¹ groups are preferablyethyl or more especially methyl groups.

Groups R⁷ and R⁸ in the B groups --SO₂ NR⁷ R⁸, --PO(NR⁷ R⁸)₂ and --SO₂R⁷ are preferably non-labile hydrogen or branched or linear C₁₋₆ alkyl(especially C₁₋₃ alkyl) optionally mono or polyhydroxylated and/or monoor poly C₁₋₃ -alkoxylated or substituted by aryl, e.g. phenyl, groups.

Aryl and arylene groups present in the compounds of the invention arepreferably mono or bicyclic containing. 5 to 7 ring atoms in the or eachring, and where the groups are heterocyclic each ring preferablycontains 1 or 2 ring heteroatoms selected from O, N and S.

The lipophilic groups M mentioned above may be any of the groupsconventionally used to increase the lipophilicity of a molecule andpreferably include aryl groups such as benzyl or phenyl groups, alkarylgroups and saturated branched or unbranched acyclic hydrocarbon groups(e.g. alkyl groups), especially such groups containing from 6 to 22,particularly 8 to 20 and more particularly 12 to 18 carbon atoms. Aspreviously mentioned, it is especially preferred that any lipophilicgroup be linked by a readily hydrolysable linkage. Ester linkages areparticularly preferred in this regard and thus preferred lipophilicgroups M include the following: ##STR1## (where s represents an integerof 1 to 3 and R¹⁰ represents hydrogen or an optionally hydroxyl oralkoxy substituted alkyl group).

Where the compounds of formulae I or Ic are linear, or branched (ie.where they contain no linking group (CR¹ R²)_(n) X¹ !_(p) (CR¹ R²)_(n))it is preferred that the B groups occur at terminal A groups.

Linear compounds of Formulae I or Ic carrying two B groups, one at eachterminus, are especially preferred. Moreover, in such linear compounds,it is particularly preferred that the two B groups be the same.

In macrocyclic compounds of formulae I or Ic it is preferred that one,two or three of the macrocyclic X groups include B groups. Suchmacrocyclic compounds moreover preferably contain 3, 4 or 5, especially4, heteroatoms in the macrocyclic ring skeleton. DO3A derivatives areespecially preferred.

The compounds of formulae I or Ic where Y is a carboxyl group canconveniently form salts or chelates in which Y represents --COOMt(wherein Mt⁺ is a monovalent cation or a fraction of a polyvalentcation, for example an ammonium or substituted ammonium ion or a metalion, for example an alkali metal or alkaline earth metal ion).Particularly preferably, Mt+ is a cation deriving from an organic base,for example meglumine or lysine. In such salts or chelates one or more(but not necessarily all) of the carboxyl groups are transformed intoCOOMt groups.

It is particularly preferred that the number of the ion-forming groups Yin the compounds of formulae I or Ic be chosen to equal the valency ofthe metal species to be chelated by the compound of formula I or Ic.Thus, for example, where Gd(III) is to be chelated, the compound offormulae I or Ic (or salt thereof) preferably contains three ion-formingY groups, for example --COOH (or --COOMt). In this way, the metalchelate will be formed as a neutral species, a form preferred since theosmolalities in concentrated solutions of such compounds are low andsince their toxicities relative to their ionic analogues aresignificantly reduced.

Particularly preferred compounds according to the invention includenon-ionic metal chelates, especially paramagnetic metal chelates, ofcompounds of formulae I or Ic in which the donor (coordinating) atomsare APCA skeleton nitrogens and Y group oxyacid (e.g. carboxylate)oxygens and especially those in which the B groups do not function ascharged, metal coordinating moieties. More especially, the compounds offormulae I or Ic preferably contain at least two non-ionizable B groups.By non-ionizable it is meant that in aqueous solution at physiologicalpH the group is substantially uncharged. Accordingly it is particularlypreferred that the compounds of formulae I or Ic and their metalchelates should contain at least one, preferably at least two, B groupswhich contain no protons having a pKa of less than 8, particularlypreferably none having pKa's of less than 8.5 or more especially 9 or9.5. Thus such B groups preferably do not contain labile hydrogens. Inchelate complexes of the compounds of formulae I or Ic these B groups,which preferably are the only B groups present, will not function ascharged donor groups for the chelated metal ions but may participate inmetal coordination and in the bonding of solvent water molecules in thefirst co-ordination sphere and thereby in the transfer of magneticinformation and consequently they are important in the realisation ofenhanced relaxivity.

Enhanced relaxivity for MRI contrast agents enables lower dosages to beused in order to achieve a particular contrast effect thus increasingthe safety margin for the MRI investigation. The hydroxamate chelatesaccording to the present invention are especially attractive in thisregard and appear to represent a particularly improved class of thirdgeneration CNS agents.

Especially preferred compounds according to the invention include thoseof formulae Ia and Ib ##STR2## where q is 0, 1 or 2, preferably 1, t is1 or 2, preferably 1, and Y¹ is an ion forming Y group, preferably acarboxyl or carboxylate group.

In the compounds of formulae Ia and Ib, the following are preferred asidentities for B

--CO--NH--NH₂

--CO--NH--N(CH₃)₂

--CO--NCH₃ --NH₂

--CO--NCH₃ --N(CH₃)₂

--CO--NR^(7') --OR^(8')

--CO--NCH₃ --OR^(8')

--SO₂ N(CH₃)₂

--PO(N(CH₃)₂)₂

--SO₂ CH₃

--NO₂

where R^(7') is an optionally substituted alkyl or aryl group or alipophilic group M and R^(8') is hydrogen, methyl, benzyl, or ##STR3##or (CH₃)₃ CCOOCHR¹⁰ --(where R¹⁰ is as defined above) the phenylmoieties of which are optionally substituted by hydroxy, alkoxy,alkoxyalkyl, hydroxyalkyl, hydroxyalkoxy or alkoxyalkoxy groups.

Particularly preferred compounds according to the invention includederivatives of DTPA and DO3A of formulae Ia' and Ib' ##STR4## whereR^(7") is a lipophilic group, eg. an alkyl, aryl, aralkyl or alkarylgroup, and R^(8') is as defined above, and preferably R^(8') ishydrogen.

The compounds of the invention may be prepared by reacting a reactivederivative of the corresponding aminopolycarboxylic acid with anappropriately substituted hydroxylamine or hydrazide, or by reacting acorresponding amine with an appropriately substituted alkylating agent.

Suitable reactive derivatives include anhydrides and esters.

Thus viewed from a further aspect the present invention provides aprocess for the preparation of compounds according to the invention,said process comprising one or more of the following steps

(i) reacting a compound of formula II

    A" X"(CR.sup.1" R.sup.2").sub.n X"!.sub.m A"               (II)

(where X" is a group X, a protected group X or a group

NA"';

A" is a group A, a protected group A or a group A"';

A"' is an alkyl group attached to an activated carboxyl or phosphonogroup;

R^(1") and R^(2") are each groups R¹ or R² or protected groups R¹ and R²respectively;

with the proviso that at least one group A"', and preferably at leasttwo such groups, is/are present)

with an amine derivative of formula III

    B"H                                                        (III)

(where B" is a group NR⁷ (OR⁸), NR⁷ NR⁸ ₂ or NR⁷ R⁸ or a protected suchgroup), followed if required by the removal of any protecting groups;

(ii) reacting a compound of formula IV

    A* X*(CR.sup.1" R.sup.2").sub.n X*!.sub.m A*               (IV)

(where A* is a group A, a protected group A or a hydrogen atom;

X* is a group X, a protected group X or a group NA*, and R^(1"), R^(2"),n and m are as hereinbefore defined, with the proviso that at least oneA*, preferably two, is hydrogen) with a compound of formula V

    Lv--A**                                                    (V)

(where Lv is a leaving group, e.g. a halogen atom, and A** is aY-containing A or protected A group) followed if required by removal ofany protecting groups;

(iii) converting a compound of formula I into a salt thereof or a saltof a compound of formula I into the free acid or base; and

(iv) converting a compound of formula I or salt thereof into a chelatecomplex thereof.

The starting compounds of formulae II and III mentioned above are eitherknown from the literature, for example the patent publications from 1983of Salutar Inc, Nycomed AS, Bracco, Guerbet, Schering, Squibb andMallinckrodt such as those mentioned above and the documents mentionedtherein, or may be prepared from known compounds by standard procedures.

The activated carboxyl and phosphono groups in the compounds of formulaII may be any derivatives capable of reacting with an amine to produce apeptide or phosphonamide linkage, e.g. an acid anhydride or acid halidegroup. These may be generated by conventional techniques.

Thus for example cyclic acid anhydrides and their cyclic amidederivatives and APCA esters may be used as the starting materials offormulae II and III as exemplified by the following reaction schemes:##STR5## where R¹⁶ and R¹⁷ are substituent groups desired to beintroduced, R¹⁸ is a halogen atom and R¹⁹ is a halogen atom or an alkoxyor acyl group.

The substituents not taking part in amide linkage formation may ofcourse require protection, eg. hydroxyl groups may need to be convertedto ester groups, during the initial reaction in step (i). Conventionalprotection and deprotection techniques may be used, see for example"Protective Groups in Organic Synthesis" by T. W. Greene,Wiley-Interscience, NY, 1981 and "Protective Groups in OrganicChemistry" by J. F. W. McOmie, Plenum, London, 1973.

Salt and chelate formation may be effected by conventional techniques,e.g. as described in the above mentioned patent publications.

The chelants of formula I may be used as the basis for bifunctionalchelants or for polychelant compounds, that is compounds containingseveral independent chelant groups, by substituting for one A, A¹, R¹,R², R⁷ or R⁸ group a bond or linkage to a macromolecule or polymer, e.g.a tissue specific biomolecule or a backbone polymer such as polylysineor polyethyleneimine which may carry several chelant groups and mayitself be attached to a macromolecule to produce abifunctional-polychelant. Such macromolecular derivatives of thecompounds of formula I and the metal chelates and salts thereof form afurther aspect of the present invention.

The linkage of a compound of formula I to a macromolecule or backbonepolymer may be effected by the methods of Salutar (WO-A-90/12050) or byany of the conventional methods such as the carbodiimide method, themixed anhydride procedure of Krejcarek et al. (see Biochemical andBiophysical Research Communications 77: 581 (1977)), the cyclicanhydride method of Hnatowich et al. (see Science 220: 613 (1983) andelsewhere), the backbone conjugation techniques of Meares et al. (seeAnal. Biochem. 142: 68 (1984) and elsewhere) and Schering (seeEP-A-331616 for example) and by the use of linker molecules as describedfor example by Nycomed in WO-A-89/06979.

Salt and chelate formation may be performed in a conventional manner.The chelating agents of formula I are particularly suitable for use indetoxification or in the formation of metal chelates, chelates which maybe used for example in or as contrast agents for in vivo or in vitromagnetic resonance (MR), X-ray or ultrasound diagnostics (e.g. MRimaging and MR spectroscopy), or scintigraphy or in or as therapeuticagents for radiotherapy, and such uses of these metal chelates form afurther aspect of the present invention.

Salts or chelate complexes of the compounds of the invention containinga heavy metal atom or ion are particularly useful in diagnostic imagingor therapy. Especially preferred are salts or complexes with metals ofatomic numbers 20-32, 42-44, 49 and 57 to 83, especially Gd, Dy and Yb.For use as an MR-diagnostics contrast agent, the chelated metal speciesis particularly suitably a paramagnetic species, the metal convenientlybeing a transition metal or a lanthanide, preferably having an atomicnumber of 21-29, 42, 44 or 57-71. Metal chelates in which the metalspecies is Eu, Gd, Dy, Ho, Cr, Mn or Fe are especially preferred andGd³⁺, Mn²⁺ and Dy³⁺ are particularly preferred. Chelates of ions ofthese metals specifically listed above with chelants of formula I ortheir salts with physiologically tolerable counterions are particularlyuseful for the diagnostic imaging procedures mentioned herein and theyand their use are deemed to fall within the scope of the invention andreferences to chelates of compounds of formula I herein are consequentlyto be taken to include such chelates.

For diagnostic imaging purposes it is particularly important that themetal chelate complex be as stable as possible to prevent dissociationof the complex in the body. It is noted in this regard that thehydroxamate and hydrazide derivatives of the invention form particularlystable complexes with the metal ions of greatest interest in MRI andthus such chelates are particularly suitable for use as diagnosticimaging contrast agents.

In magnetic resonance imaging (MRI) it is frequently desirable to beable to target certain organs or tissues. In particular there is a needfor improved hepatobiliary imaging MR contrast agents. Chelates ofparamagnetic metals with compounds of formula I where one or more of theR⁷ or R⁸ groups in the groups COB are lipophilic groups M areparticularly suited for use as hepatobiliary MR contrast agents, sincethe presence of the lipophilic group will promote uptake by hepatocytes.By linking the lipophilic group to the molecule via a readilyhydrolysable linking group such as an ester, the reabsorption afterexcretion to the intestine can be prevented.

For certain hepatobiliary imaging purposes it is desirable that thelipophilic contrast agent be precipitated as particles which can betaken up by Kupffer cells in the liver. In such cases it is preferred touse chelates of Dy³⁺ with lipophilic compounds of formula I inconjunction with an imaging system utilising the magnetic susceptibilityproperties of the contrast agent; Kupffer cells in the liver are scarceand the contrast achievable using chelates with the gadolinium normallyused in conventional MR imaging (i.e. as a T₁ relaxation agent) isgenerally insufficient. Such magnetic susceptibility agents form animportant embodiment of the invention.

For use as contrast agents in MRI, the paramagnetic metal species isconveniently non-radioactive as radioactivity is a characteristic whichis neither required nor desirable for MR-diagnostic contrast agents. Foruse as X-ray or ultrasound contrast agents, the chelated metal speciesis preferably a heavy metal species, for example a non-radioactive metalwith an atomic number greater than 37, preferably greater than 50, e.g.Dy³⁺.

For use in scintigraphy and radiotherapy, the chelated metal speciesmust of course be radioactive and any conventional complexableradioactive metal isotope, such as ^(99m) Tc, ⁶⁷ Ga or ¹¹¹ In forexample, may be used. For radiotherapy, the chelating agent may be inthe form of a metal chelate with for example ¹⁵³ Sm, ⁶⁷ Cu or ⁹⁰ Y.

For use in detoxification of heavy metals, the chelating agent should bein salt form with a physiologically acceptable counterion, e.g. sodium,calcium, ammonium, zinc or meglumine, e.g. as the sodium salt of thechelate of the compound of formula I with zinc or calcium.

Where the metal chelate carries an overall charge, such as is the casewith the prior art Gd DTPA, it will conveniently be used in the form ofa salt with a physiologically acceptable counterion, for example anammonium, substituted ammonium, alkali metal or alkaline earth metal(e.g. calcium) cation or an anion deriving from an inorganic or organicacid. In this regard, meglumine salts are particularly preferred.

Viewed from a further aspect, the present invention provides adiagnostic or therapeutic agent comprising a metal chelate, whereof thechelating entity is the residue of a compound according to the presentinvention, together with at least one pharmaceutical or veterinarycarrier or excipient, or adapted for formulation therewith or forinclusion in a pharmaceutical formulation for human or veterinary use.

Viewed from another aspect, the present invention provides adetoxification agent comprising a chelating agent according to theinvention in the form of a weak complex or salt with a physiologicallyacceptable counterion, together with at least one pharmaceutical orveterinary carrier or excipient, or adapted for formulation therewith orfor inclusion in a pharmaceutical formulation for human or veterinaryuse.

The diagnostic and therapeutic agents of the present invention may beformulated with conventional pharmaceutical or veterinary formulationaids, for example stabilizers, antioxidants, osmolality adjustingagents, buffers, pH adjusting agents, etc. and may be in a form suitablefor parenteral or enteral administration, for example injection orinfusion or administration directly into a body cavity having anexternal escape duct, for example the Gastrointestinal tract, thebladder or the uterus. Thus the agent of the present invention may be ina conventional pharmaceutical administration form such as a tablet,capsule, powder, solution, suspension, dispersion, syrup, suppository,etc; however, solutions, suspensions and dispersions in physiologicallyacceptable carrier media, for example water for injections, willgenerally be preferred.

The compounds according to the invention may therefore be formulated foradministration using physiologically acceptable carriers or excipientsin a manner fully within the skill of the art. For example, thecompounds, optionally with the addition of pharmaceutically acceptableexcipients, may be suspended or dissolved in an aqueous medium, with theresulting solution or suspension then being sterilized. Suitableadditives include, for example, physiologically biocompatible buffers(as for example, tromethamine hydrochloride), additions (e.g. 0.01 to 10mole percent) of chelants (such as, for example, DTPA, DTPA-bisamide ornon-complexed chelants of formula I) or calcium chelate complexes (asfor example calcium DTPA, CaNaDTPA-bisamide, calcium salts or chelatesof chelants of formula I), or, optionally, additions (e.g. 1 to 50 molepercent) of calcium or sodium salts (for example, calcium chloride,calcium ascorbate, calcium gluconate or calcium lactate combined withmetal chelate complexes of chelants of formula I and the like).

If the compounds are to be formulated in suspension form, e.g., in wateror physiological saline for oral administration, a small amount ofsoluble chelate may be mixed with one or more of the inactiveingredients traditionally present in oral solutions and/or surfactantsand/or aromatics for flavouring.

For MRI and for X-ray imaging of some portions of the body the mostpreferred mode for administering metal chelates as contrast agents isparenteral, e.g. intravenous administration. Parenterally administrableforms, e.g. intravenous solutions, should be sterile and free fromphysiologically unacceptable agents, and should have low osmolality tominimize irritation or other adverse effects upon administration, andthus the contrast medium should preferably be isotonic or slightlyhypertonic. Suitable vehicles include aqueous vehicles customarily usedfor administering parenteral solutions such as Sodium ChlorideInjection, Ringer's Injection, Dextrose Injection, Dextrose and SodiumChloride Injection, Lactated Ringer's Injection and other solutions suchas are described in Remington's Pharmaceutical Sciences, 15th ed.,Easton: Mack Publishing Co., pp. 1405-1412 and 1461-1487 (1975) and TheNational Formulary XIV, 14th ed. Washington: American PharmaceuticalAssociation (1975). The solutions can contain preservatives,antimicrobial agents, buffers and antioxidants conventionally used forparenteral solutions, excipients and other additives which arecompatible with the chelates and which will not interfere with themanufacture, storage or use of products.

Where the diagnostic or therapeutic agent comprises a chelate or salt ofa toxic metal species, e.g. a heavy metal ion, it may be desirable toinclude within the formulation a slight excess of the chelating agent,e.g. as discussed by Schering in DE-A-3640708, or more preferably aslight excess of the calcium salt of such a chelating agent.

For MR-diagnostic examination, the diagnostic agent of the presentinvention, if in solution, suspension or dispersion form, will generallycontain the metal chelate at concentration in the range 1 micromole to1.5 mole per liter, preferably 0.1 to 700 mM. The diagnostic agent mayhowever be supplied in a more concentrated form for dilution prior toadministration. The diagnostic agent of the invention may convenientlybe administered in amounts of from 10⁻³ to 3 mmol of the metal speciesper kilogram of body weight, e.g. about 1 mmol Dy/kg bodyweight.

For X-ray examination, the dose of the contrast agent should generallybe higher and for scintigraphic examination the dose should generally belower than for MR examination. For radiotherapy and detoxification,conventional dosages may be used.

Viewed from a further aspect, the present invention provides a method ofgenerating enhanced images of the human or non-human animal body, whichmethod comprises administering to said body a diagnostic agentcomprising a metal chelate of compound of formula I

    A  X(CR.sup.1 R.sup.2).sub.n !.sub.m XA                    (I)

(wherein in formula I,

each of the groups R¹ and R² may independently represent a hydrogen atomor an alkyl or alkoxy group, optionally carrying one or moresubstituents selected from hydroxy, alkoxy and aryl groups;

each X independently represents an oxygen or sulphur atom or,preferably, a group NA;

each A independently represents a hydrogen atom or an alkyl groupoptionally substituted by a group Y;

or one or more pairs of A groups on different X moieties may togetherform a group (CR¹ R²)_(n) X¹ !_(p) (CR¹ R²)_(n) or a group A on amid-chain nitrogen may represent a group (CR¹ R²)_(n) X¹ !_(p) (CR¹R²)_(n) X¹ A where p represents an integer of 0 to 6, preferably 0, andeach X¹ independently represents an oxygen or sulphur atom or a groupNA¹ where A¹ is as defined for A but may not form part of a groupattached to more than one nitrogen atom;

or two adjacent groups R¹ and/or A may together form a homo- orheterocyclic saturated or unsaturated 5-7 membered ring containing 0, 1or 2 ring heteroatoms selected from oxygen, nitrogen and sulphur;

each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R⁶, CSZ, PO₂ Zor B;

each group B represents a group CONR⁷ (OR⁸), CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂,SO₂ NR⁷ R⁸, SO₂ R⁷ or NO₂ ;

each group Z independently represents a group OR⁶, SR⁶ or NR⁶ ₂ ;

each of the groups R⁶ independently represents a hydrogen atom, or analkyl group optionally substituted by one or more hydroxy or alkoxygroups;

each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups or a lipophilic group M, preferably incorporating or linked via ahydrolysable (e.g. ester) linkage;

m is an integer of 2 to 8, preferably 2, 3 or 4;

n is an integer of 2 to 4, preferably 2 or 3, especially 2;

with the provisos that where the compound of formula I is linear andeach X is NA and two terminal A groups carry Y groups of formulaCON(OR⁸)R⁷, then in said terminal A groups (i) if R⁸ is hydrogen R⁷ isother than methyl (preferably other than hydrogen or unsubstitutedalkyl, especially C₁₋₃ alkyl) and (ii) if R⁷ is alkoxylated alkyl R⁸ isother than methyl (preferably other than unsubstituted alkyl), and thatat least two, preferably at least three, ionisable non-B Y groups arepresent and that at least one Y group represents a non-ionizable groupB).

Viewed from a further aspect, the present invention provides a method ofradiotherapy practised on the human or non-human animal body, whichmethod comprises administering to said body a chelate of a radioactivemetal species with a chelating agent of formula I

    A X(CR.sup.1 R.sup.2).sub.n !.sub.m XA                     (I)

(wherein in formula I,

each of the groups R¹ and R² may independently represent a hydrogen atomor an alkyl or alkoxy group, optionally carrying one or moresubstituents selected from hydroxy, alkoxy and aryl groups;

each X independently represents an oxygen or sulphur atom or,preferably, a group NA;

each A independently represents a hydrogen atom or an alkyl groupoptionally substituted by a group Y;

or one or more pairs of A groups on different X moieties may togetherform a group (CR¹ R²)_(n) X¹ !_(p) (CR¹ R²)_(n) or a group A on amid-chain nitrogen may represent a group (CR¹ R²)_(n) X¹ !_(p) (CR¹R²)_(n) X¹ A where p represents an integer of 0 to 6, preferably 0, andeach X¹ independently represents an oxygen or sulphur atom or a groupNA¹ where A¹ is as defined for A but may not form part of a groupattached to more than one nitrogen atom;

or two adjacent groups R¹ and/or A may together form a homo- orheterocyclic saturated or unsaturated 5-7 membered ring containing 0, 1or 2 ring heteroatoms selected from oxygen, nitrogen and sulphur;

each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R⁶, CSZ, PO₂ Zor B;

each group B represents a group CONR⁷ (OR⁸), CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂,SO₂ NR⁷ R⁸, SO₂ R⁷ or NO₂ ;

each group Z independently represents a group OR⁶, SR⁶ or NR⁶ ₂ ;

each of the groups R⁶ independently represents a hydrogen atom, or analkyl group optionally substituted by one or more hydroxy or alkoxygroups;

each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups or a lipophilic group M, preferably incorporating or linked via ahydrolysable (e.g. ester) linkage;

m is an integer of 2 to 8, preferably 2, 3 or 4;

n is an integer of 2 to 4, preferably 2 or 3, especially 2;

with the provisos that where the compound of formula I is linear andeach X is NA and two terminal A groups carry Y groups of formulaCON(OR⁸)R⁷, then in said terminal A groups (i) if R⁸ is hydrogen R⁷ isother than methyl (preferably other than hydrogen or unsubstitutedalkyl, especially C₁₋₃ alkyl) and (ii) if R⁷ is alkoxylated alkyl R⁸ isother than methyl (preferably other than unsubstituted alkyl), and thatat least two, preferably at least three, ionisable non-B Y groups arepresent and that at least one Y group represents a non-ionizable groupB).

Viewed from a further aspect, the present invention provides a method ofheavy metal detoxification practised on the human or non-human animalbody, which method comprises administering to said body a chelatingagent of formula I

    A X(CR.sup.1 R.sup.2).sub.n !.sub.m XA                     (I)

(wherein in formula I,

each of the groups R¹ and R² may independently represent a hydrogen atomor an alkyl or alkoxy group, optionally carrying one or moresubstituents selected from hydroxy, alkoxy and aryl groups;

each X independently represents an oxygen or sulphur atom or,preferably, a group NA;

each A independently represents a hydrogen atom or an alkyl groupoptionally substituted by a group Y;

or one or more pairs of A groups on different X moieties may togetherform a group (CR¹ R²)_(n) X¹ !_(p) (CR¹ R²)_(n) or a group A on amid-chain nitrogen may represent a group (CR¹ R²)_(n) X¹ !_(p) (CR¹R²)_(n) X¹ A where p represents an integer of 0 to 6, preferably 0, andeach X¹ independently represents an oxygen or sulphur atom or a groupNA¹ where A¹ is as defined for A but may not form part of a groupattached to more than one nitrogen atom;

or two adjacent groups R¹ and/or A may together form a homo- orheterocyclic saturated or unsaturated 5-7 membered ring containing 0, 1or 2 ring heteroatoms selected from oxygen, nitrogen and sulphur;

each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R⁶, CSZ, PO₂ Zor B;

each group B represents a group CONR⁷ (OR⁸), CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂,SO₂ NR⁷ R⁸, SO₂ R⁷ or NO₂ ;

each group Z independently represents a group OR⁶, SR⁶ or NR⁶ ₂ ;

each of the groups R⁶ independently represents a hydrogen atom, or analkyl group optionally substituted by one or more hydroxy or alkoxygroups;

each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups or a lipophilic group M, preferably incorporating or linked via ahydrolysable (e.g. ester) linkage;

m is an integer of 2 to 8, preferably 2, 3 or 4;

n is an integer of 2 to 4, preferably 2 or 3, especially 2;

with the provisos that where the compound of formula I is linear andeach X is NA and two terminal A groups carry Y groups of formulaCON(OR⁸)R⁷, then in said terminal A groups (i) if R⁸ is hydrogen R⁷ isother than methyl (preferably other than hydrogen or unsubstitutedalkyl, especially C₁₋₃ alkyl) and (ii) if R⁷ is alkoxylated alkyl R⁸ isother than methyl (preferably other than unsubstituted alkyl), and thatat least two, preferably at least three, ionisable non-B Y groups arepresent and that at least one Y group represents a non-ionizable groupB), or a physiologically tolerable salt or weak complex thereof.

Preferred for use in such methods are compounds of Formula I, Ia, Ib,Ia', Ib' and Ic, as defined above with the provisos that where thecompound of formula I is linear and each X is NA and two terminal Agroups carry Y groups of formula CON(OR⁸)R⁷, then in said terminal Agroups (i) if R⁸ is hydrogen R7 is other than methyl (preferably otherthan hydrogen or unsubstituted alkyl, especially C₁₋₃ alkyl) and (ii) ifR⁷ is alkoxylated alkyl R⁸ is other than methyl (preferably other thanunsubstituted alkyl), and that at least two, preferably at least three,ionisable non-B Y groups are present and that at least one Y grouprepresents a non-ionizable group B).

Viewed from a yet further aspect, the present invention also providesthe use of the compounds, especially the metal chelates, according tothe invention for the manufacture of diagnostic or therapeutic agentsfor use in methods of image generation, detoxification or radiotherapypractised on the human or non-human animal body.

Viewed from a still further aspect, the present invention provides aprocess for the preparation of the metal chelates of the invention whichprocess comprises admixing in a solvent a compound of formula I or asalt (e.g. the sodium salt) or chelate thereof together with an at leastsparingly soluble compound of said metal, for example a chloride, oxide,acetate or carbonate.

Viewed from a yet still further aspect, the present invention provides aprocess for the preparation of the diagnostic or therapeutic agent ofthe present invention, which comprises admixing a metal chelateaccording to the invention, or a physiologically acceptable saltthereof, together with at least one pharmaceutical or veterinary carrieror excipient.

Viewed from a yet still further aspect, the present invention provides aprocess for the preparation of the detoxification agent of theinvention, which comprises admixing a chelating agent according to theinvention, preferably in the form of a salt with a physiologicallyacceptable counterion, together with at least one pharmaceutical orveterinary carrier or excipient.

The disclosures of all of the documents mentioned herein areincorporated by reference.

The present invention will now be illustrated further by the followingnon-limiting Examples. All ratios and percentages given herein are byweight and all temperatures are in degrees Celsius unless otherwiseindicated.

EXAMPLES Example 1 DTPA-TMDX ##STR6##

N,O-Dimethylhydroxylamine hydrochloride (16.0 g/164 mmol) was added todry acetonitrile (60 ml) together with diisopropylethylamine (34.5ml/198 mmol). The solution was stirred at ambient temperature until theamines were dissolved (10 minutes). DTPA bisanhydride (6.0 g/16.8 mmol)was then added in portions over 2 minutes. 10 minutes after additionended, all the anhydride had gone into solution. The mixture was stirredovernight, and acetic acid (11.4 ml/198 mmol) was then added. Themixture was evaporated down to an oily residue which was dissolved inwater and applied on an AG1-X8 ion exchange column (acetate form) at pH9.5. The column was washed with water before the product was eluted with0.5M acetic acid. The chromatographic procedure was repeated twice togive the title compound. Yield 3.5 g, (43% of theory). The white solidwas recrystalized twice from IPA.

¹ H NMR (D₂ O): CH₃ --0 3.48 (s, 6H); CH₃ --N 2.98 (s, 6H); N--CH₂--CO4.4 (s, 4H), 3.62 (s, 4H), 3.29 (s, 2H); N--CH₂ --CH₂ --N 2.9 (m,4H), 3.3 (m, 4H).

Water: 4.0%.

Titration: Purity about 98%.

FAB-MS: MH+: 480 (83%), 422 (17%), 203 (100%).

Example 2 Gd-DTPA-TMDX

DTPA-TMDX (50 mg/0.104 mmol) was dissolved in water (2.0 ml) andGdCl₃.6H₂ O (36 mg/0.97 mmol) in water (3 ml) was added. The pH wasadjusted to 6.74 with 2N NaOH, and the sample was lyophilized to givethe title compound. Relaxivity R₁ =4.21 mmol⁻¹ sec⁻¹ and R₂ =5.14 mmol⁻¹sec⁻¹ in water at 10 MHz, 37° C.

Example 3 DTPA-TMHZ ##STR7##

1,1-Dimethylhydrazine (6.1 ml/80.6 mmol) and diisopropylethylamine (17.6ml/101 mmol) were dissolved in dry acetonitrile (400 ml) at ambienttemperature. DTPA bisanhydride (12.0 g/33.6 mmol) was added as a powderin portions over 10 minutes under a N₂ atmosphere and with mechanicalstirring. The solution was stirred overnight. Diethylether (600 ml) wasthen added dropwise, and the mixture was stirred for an additional 24hours before the solvents were decanted off. The remaining precipitatewas dissolved in water to a volume of 150 ml. The pH was adjusted to 9with 2N NaOH, and the solution was applied on an AG1-X8 ion exchangecolumn (acetate form). After washing of the column with water (2900 ml),the product was eluted with 0.5M acetic acid. Collected fractionscontaining the product were combined and lyophilized to yield 9.2 g(57%) of the title compound. The material was recrystallized twice fromwater/IPA/acetone.

¹ H-NMR (D₂ O,pH6.8): δ 2.29 (s, 12H); 2.82(t,4H); 2.97 (s, 4H); 3.07(t,4H); 3.13 (s, 4H); 3.55 (s, 2H). FAB-MS: MH+: 478 (100%), 420 (20%)202 (70%).

Example 4 Gd-DTPA-TMHZ

DTPA-TMHZ (50 mg/0.104 mmol) was dissolved in water (2.0 ml) andGdCl₃.6H₂ O (35 mg/0.94 mmol) in water (3 ml) was added. The pH wasadjusted to 6.68 with 2N NaOH, and the sample was lyophilized to givethe title compound. Relaxivity R₁ =4.86 mmol⁻¹ sec⁻¹ and R₂ =5.40 mmol⁻¹sec⁻¹ in water at 10 MHz, 37° C.

Example 5 DTPA(DEHZ)₂ ##STR8##

1,2-Diethyl hydrazine dihydrochloride (1.61 g, 10 mmol) anddiisopropylethylamine (4.52 g, 35 mmol) are dissolved in dryacetonitrile (50 ml) at ambient temperature. DTPA bisanhydride (2.95 g,8.25 mmol) is added as a powder in portions over 10 minutes under an N₂atmosphere. The solution is stirred overnight. Diethyl ether (75 ml) isthen added dropwise, this mixture is stirred an additional 24 hours andthe solvents decanted; the remaining precipitate is dissolved in water(20 ml). The pH adjusted to 9 with 2N NaOH and the solution is appliedto AG1-X8 ion exchange column (acetate form). After washing with waterthe product is eluted with 0.5M acetic acid.

Example 6 O-Bz-DTPA-DX ##STR9##

O-Benzylhydroxylamine (4.47 g/28 mmol) was stirred at ambienttemperature in dry acetonitrile (150 ml) together withdiisopropylethylamine (6.5 ml/37 mmol) until a clear solution wasobtained (0.5 hours). DTPA bisanhydride (1.0 g/2.8 mmol) was added as apowder, and the resulting mixture was stirred overnight. Acetic acid(2.2 ml/37 mmol) was added and the solution was evaporated to an oilyresidue which was dissolved in water. The pH was adjusted to 0.5 with 2NNaOH and the mixture was applied on an AG1-X8 ion exchange column(acetate form). The column was flushed with water (1000 ml) and 0.5Nacetic acid (600 ml) before the product was eluted with 2N acetic acid.The fractions containing the product were rechromatographed using 1Nacetic acid in methanol:water (1:1 by volume) as eluent to give thetitle compound (50 mg).

¹ H-NMR (D₂ O): Ph--H7.17 (s); Ar--CH₂ 4.65 (s); N--CH₂ --CO 3.4-3.5;N--CH₂ --CH₂ --N 2.6-3.0 (m).

Example 7 Relaxivity of DTPA-DX-(2-isopropyl)₂ ##STR10##

The relaxivity of Gd DTPA-DX-(2-isopropyl)₂ (prepared as described forexample by Turowski et al. in Inorganic Chemistry 27:474-481(1988)) inwater at a concentration range of 16 mM to 0.08 mM was determined to be6.7 mM⁻¹ s⁻¹. Measurements were performed at 10 MHz and 37° C.

Example 8 O-Bz-EDTA-DX ##STR11##

5N NaOH (50 ml) was poured into a 125 ml separating funnel.O-Benzyl-hydroxylamine-HCl (11.2 g/0.07 mol) was added and extractedwith CH₂ Cl₂ (3×35 ml). The extract was washed with water, dried withNa₂ SO₄ and concentrated to an oil in a rotovap. The oil was dilutedwith pyridine, EDTA-bisanhydride (7.7 g/0.03 mol) was added and themixture was stirred using a stir bar under N₂. The pyridine was removedusing a rotovap (65° C., pump). The glassy residue was dissolved in hotIPA (100 ml). The solvent was removed under vacuum yielding a foamysolid which was dissolved in hot IPA (150 ml). Ethyl acetate (400 ml)was added forming a gummy precipitate. The supernatant was decanted anddiethylether was stirred into it and the mixture was chilled. The whiteprecipitate formed (the "second crop") was filtered and dried (6 g). Thegummy precipitate was dissolved in methanol (150 ml) and cooled. Ethylacetate (100 ml) and diethylether (100 ml) were added and the mixturewas allowed to stand for 30 minutes. The precipitate formed was filteredand dried (6 g). One gram of the second crop was used for ahydrogenolysis experiment. The remaining dried precipitate (ca. 12 g)was dissolved in hot methanol (ca. 100 ml) and filtered. Ethyl acetate(200 ml) was added and the mixture was stirred for 2 hours. Theprecipitate was filtered and dried in vacuo. Yield: 10 g. Mpt. 117°-119°C.

Example 9 ##STR12## O-Benzylhydroxamic acid DO3A

a) Cyclen

1,4,7,10-Tetrazacyclodecane tetrahydrochloride (66.6 g, 209 mmol) wassuspended in CHCl₃ (2L) and ammonia gas was bubbled through the solutionfor 1 hour. The solution was allowed to stir overnight. The white solidwas filtered off and was washed with four 100 mL portions of CHCl₃. Thefiltrate was combined with the CHCl₃ washings and was concentrated byrotary evaporation. The resulting white solid was washed with four 50 mLportions of diethyl ether and was dried under vacuum to give the titlecompound (31.5 g). A second crop (3.7 g) could be obtained byconcentrating the ether washings.

¹ H-NMR (CDCl₃): N--CH₂ --CH₂ --N 2.71 (4H, s); N--H2.35 (1H, s).

b) 1,4,7,10-Tetrazacyclodecane-4,7,10-triacetic acid tri-t-butyl estermonohydrobromide salt

Sodium acetate (50.0 g, 609 mmol) was added to a stirred suspension ofcyclen (35.0 g, 203 mmol) in N,N-dimethylacetamide (DMA) (600 mL) atambient temperature. After 0.5 hours, a solution of t-butylbromoacetate(118.9 g, 609 mmol) in DMA (150 mL) was added dropwise under N₂. Themixture was stirred at ambient temperature under N₂ for 19 days. Thewhite solid was collected by filtration, was washed with ice-cold DMA(75 mL) and ethyl acetate (100 mL), and was dried under vacuum at 50° C.to give 80.2 g of product plus sodium acetate. A second crop of 38.4 gcould be collected by concentrating the filtrate to approximately 500 mLand isolating the solid as above. The combined solids were dissolved inCHCl₃ (600 mL) and were washed with four 100 mL portions of deionized H₂O. The CHCl₃ layer was dried over anhydrous Na₂ SO₄, filtered andconcentrated to give the title compound as a white solid (67.4 g).

¹ H-NMR (CDCl₃): NCH₂ CO₂ C(CH₃)₃ 3.22 (4H, s); NCH₂ CO₂ C(CH₃)₃ 3.23(2H, s); NCH₂ CH₂ --N 3.04 (4H, bs); N--CH₂ CH₂ --N 2.86 (m); NCH₂ CO₂(CH₃)₃ 1.40 (27H, s).

c) ClCH₂ CONHOBz

O-Benzylhydroxylamine hydrochloride (5.0 g) was treated with NaOH (5N,200 mL) and extracted with ether (200 mL). The ether layer was washedwith water, dried over anhydrous magnesium sulphate, filtered andconcentrated to yield the free base as a yellow oil (4.06 g).

¹ H-NMR (CDCl₃): 7.35 (s, Ar--H); 5.35 (br, s, NH₂); 4.68 (s, OCH₂).

O-Benzylhydroxylamine (4.06 g, 33 mmol) and triethylamine (4.7 mL, 33mmol) were dissolved in chloroform (50 mL) and cooled under nitrogen to-30° C. A solution of chloroacetylchloride (2.63 mL, 33 mmol) inchloroform (15 mL) was added dropwise over a period of 45 minutes. Thelight green solution was allowed to warm to ambient temperature andstirred for 7 hours. After the addition of water (20 mL), the organiclayer was removed and washed with saturated sodium bicarbonate solution(20 mL) and water (20 mL). The organic layer was dried over anhydrousmagnesium sulfate, filtered and concentrated to obtain the crude productas a light blue solid (6.02 g). This material was suspended in a mixtureof 1:1 ether/chloroform (100 mL) overnight, filtered and washed withether (30 mL). The solid was dried under vacuum (4.85 g, 74%).

¹ H-NMR (CDCl₃): 8.79 (br, NH); 7.39 (s, Ar--H); 4.93 (s, OCH₂); 4.03(s, COCH₂).

d) O-Benzylhydroxamic acid DO3A-tri-t-butyl ester

To a stirred solution of DO3A-tri-t-butyl ester (8.0 g, 13.4 mmol) inacetonitrile (60 mL) was added O-chloro-N-benzylhydroxamic acid (2.7 g,14.4 mmol). Tetramethylguanidine (3.3 mL, 26.9 mmol) was then addedfollowed by additional acetonitrile (50 mL). The mixture was placedunder a stream of N₂, heated to 60° C., and stirred for three days. Theresulting golden brown solution was concentrated to give a yellowresidue which was taken up in chloroform (70 mL) and washed with water(3×40 mL). The organic phase was dried (MgSO₄), filtered, andconcentrated first on a rotary evaporator and then under vacuum to yield10.6 g (116%) of a reddish brown oil.

¹ H-NMR (CDCl₃): δ (m, 12H), 2.46 (s, 4H), 1.43 (s, 9H), 1.41 (s, 18H).

e) DO3A-O-benzylhydroxamic acid

To a stirred solution of O-benzylhydroxamic acid DO3A-tri-t-butyl ester(150 mg, 0.220 mmol) in methylene chloride (4 mL) was added a mixture oftrifluoroacetic acid (8 mL) and methylene chloride (4 mL). Afterstirring for three hours at ambient temperature, the solution wasconcentrated and then redissolved in a mixture of trifluoroacetic acid(8 mL) and methylene chloride (8 mL). The solution was stirred atambient temperature for seven hours and then concentrated to give abrown oil which was chased with chloroform (4×10 mL) and then water(3×10 mL). The oil was then dissolved in 4M NaOH (10 mL) and washed withchloroform (3×10 mL). Concentration of the aqueous phase gave a thickbrown oil which was placed under vacuum to give 130 mg of a biege solid.

¹ H-NMR (D₂ O): δ 7.21 (br, 5H), 3.85-2.37 (br, 26H).

Example 10

The gadolinium chelate of O-benzylhydroxamic acid Do3A (Example 9) isprepared analogously to Example 2. Relaxivity R₁ =4.42 mmol⁻¹ sec⁻¹ andR₂ =4.62 mmol⁻¹ sec⁻¹ in water at 10 MHz, 37° C. (corresponding figuresmeasured in plasma are R₁ =5.31 and R₂ =6.77 mmol⁻¹ sec⁻¹ respectively).

We claim:
 1. A macrocyclic compound of formula I

    A(X(CR.sup.1 R.sup.2).sub.n).sub.m XA                      (I)

or a chelate complex or salt thereof, wherein in formula I, each of thegroups R¹ and R² may independently represent a hydrogen atom; each Xindependently represents a group NA; each A independently represents ahydrogen atom or an alkyl group optionally substituted by a group Y,with the proviso that one or more pairs of A groups on different Xmoieties together form a group (CR¹ R²)_(n), thereby forming amacrocyclic compound, each Y represents a hydrogen atom, or a group Z,COZ, SO₃ R⁶, CSZ, PO₂ Z, or B; each group B represents a group CONR⁷(NR⁸ ₂), PO(NR⁷ R⁸)₂, SO₂ R⁷, SO₂ NR⁷ R⁸, or NO₂ ; each group Zindependently represents a group OR⁶, SR⁶, or NR⁶ ₂ ; each of the groupsR⁶ independently represents a hydrogen atom, or an alkyl groupoptionally substituted by one or more hydroxy or alkoxy or aryl groups;each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups, or a lipophilic group; m is 3; n is an integer of 2 to 3; withthe provisos that:(1) at least two non-B ionizable Y groups are present;and (2) at least one Y group represents a non-ionizable group B.
 2. Acompound of formula I as claimed in claim 1 of formula Ib: ##STR13##where B is CONR⁷ (NR⁸ ₂) and q is 1, t is 1, and Y¹ is an ion forminggroup Y.
 3. A compound of the formula Ib as claimed in claim 2, whereinY¹ is a carboxyl or carboxylate group.
 4. A macrocyclic compound offormula Ic

    A(X(CH.sub.2).sub.2).sub.3 XA                              (Ic)

or a chelate complex or salt thereof wherein in formula Ic, each Xrepresents a group NA; each A independently represents a hydrogen atomor an alkyl group optionally substituted by a group Y, with the provisothat the two terminal A groups together form a group (CH₂)₂, therebyforming a macrocyclic compound, each Y represents a hydrogen atom, or agroup Z, COZ, SO₃ R⁶, CSZ, PO₂ Z, or B; each group B represents a groupCONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂, SO₂ R⁷, SO₂ NR⁷ R⁸, or NO₂ ; each group Zindependently represents a group OR⁶, SR⁶, or NR⁶ ₂ ; each of the groupsR⁶ independently represents a hydrogen atom, or an alkyl groupoptionally substituted by one or more hydroxy or alkoxy or aryl groups;each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups, or a lipophilic group; with the provisos that:(1) at least twonon-B ionizable Y groups are present; and (2) at least one Y grouprepresents a non-ionizable group B.
 5. A compound as claimed in claim 1,wherein R⁷ is an optionally substituted alkyl or aryl group, or alipophilic group and R⁸ is hydrogen, methyl, benzyl, ##STR14## or (CH₃)₃CCOOCHR¹⁰ --, where R¹⁰ is hydrogen or an optionally hydroxyl or alkoxysubstituted alkyl group, the phenyl moieties of which are optionallysubstituted by hydroxyl, alkoxy, alkoxyalkyl, hydroxyalkyl,hydroxyalkyl, hydroxyalkoxy, or alkoxyalkoxy groups.
 6. A macrocycliccompound as claimed in claim 4 ##STR15## wherein R⁷ is a lipophilicgroup and R⁸ is hydrogen, methyl, benzyl, ##STR16## or (CH₃)₃ CCOOCHR¹⁰--, where R¹⁰ is hydrogen or an optionally hydroxyl or alkoxysubstituted alkyl group, the phenyl moieties of which are optionallysubstituted by hydroxy, alkoxy, alkoxyalkyl, hydroxyalkyl,hydroxyalkoxy, or alkoxyalkoxy groups.
 7. A compound of claim 6 whereinR⁷ is an alkyl, aryl, aralkyl, or alkaryl group and R⁸ is hydrogen.
 8. Aprocess for the preparation of a macrocyclic compound of formula I asdefined in claim 1, said process comprising one or more of the followingsteps(i) reacting a compound of formula II

    A"(X"(CR.sup.1" R.sup.2").sub.n X").sub.m A"               (II)

where X" is a group X, a protected group X, or a group NA"'; A" is agroup A, a protected group A, or a group A"'; A"' is an alkyl groupattached to an activated carboxyl or phosphono group; R^(1") and R^(2")are each groups R¹ or R² or protected groups R¹ and R² respectively;with the proviso that at least one group A"' is present, with an aminederivative of formula III

    B"H                                                        (III)

where B" is a group, NR⁷ NR⁸ ₂, or NR⁷ R⁸ or a protected such group,followed, if required, by the removal of any protecting groups;(ii)reacting a compound of formula IV

    A*(X*(CR.sup.1" R.sup.2").sub.n X*).sub.m A*               (IV)

where A* is a group A, a protected group A or a hydrogen atom; X* is agroup X, a protected group X, or a group NA*, and R^(1"), R^(2"), n andm are as hereinbefore defined, with the proviso that at least one A* ishydrogen with a compound of formula V

    Lv--A**                                                    (V)

where Lv is a leaving group and A** is a Y-containing A or protected Agroup, followed, if required, by the removal of any protectinggroups;(iii) converting a compound of formula I into a salt thereof or asalt of a compound of formula I into the free acid or base; and (iv)converting a compound of formula I or salt thereof into a chelatecomplex thereof.
 9. A macromolecular derivative of a compound of formulaI or a metal chelate or salt thereof as defined in claim 1 in which saidcompound is linked to a macromolecule or polymer.
 10. A diagnostic agentcomprising a macrocyclic compound of formula I

    A(X(CR.sup.1 R.sup.2).sub.n).sub.m XA                      (I)

or a metal chelate of salt thereof, formulated together with or adaptedfor formulation with at least one pharmaceutical or veterinary carrieror excipient wherein in formula I each of the groups R¹ and R² mayindependently represent a hydrogen atom, or an alkyl or alkoxy groupoptionally carrying one or more substituents selected from hydroxy,alkoxy and aryl groups; each X independently represents an oxygen orsulphur atom, or a group NA; each A independently represents a hydrogenatom or an alkyl group optionally substituted by a group Y, with theproviso that one or more pairs of A groups on different X moieties maytogether form a group (CR¹ R²)_(n), thereby forming a macrocyclic ring,each Y represents a hydrogen atom, or a group Z, COZ, SO₃ R₆, CSZ, PO₂Z, or B; each group B represents a group CONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂, SO₂R⁷, SO₂ NR⁷ R⁸, or NO₂ ; each group Z independently represents a groupOR⁶, SR⁶, or NR⁶ ₂ ; each of the groups R⁶ independently represents ahydrogen atom, or a alkyl group optionally substituted by one or morehydroxy or alkoxy groups; each of the groups R⁷ and R⁸ independentlyrepresents a group R⁶, an aryl group optionally substituted by one ormore hydroxy or alkoxy groups, or a lipophilic group; m is 3; n is aninteger of 2 to 3; with the provisos that:(1) at least two non-Bionizable Y groups are present; and (2) at least one Y group representsa non-ionizable group B.
 11. A diagnostic agent as claimed in claim 10of formula Ib or a metal chelate or salt thereof ##STR17## where B isCONR⁷ (NR⁸ ₂) and q is 1, t is 1, and Y¹ is an ion forming group Y. 12.A diagnostic agent as claimed in claim 10 or a metal chelate or saltthereof ##STR18## where R⁷ is a lipophilic group and R⁸ is hydrogen,methyl, benzyl, ##STR19## or (CH₃)₃ CCOOCHR¹⁰ --, where R¹⁰ is hydrogenor an optionally hydroxyl or alkoxy substituted alkyl group, the phenylmoieties of which are optionally substituted by hydroxy, alkoxy,alkoxyalkyl, hydroxyalkyl, hydroxyalkoxy, or alkoxyalkoxy groups.
 13. Adiagnostic agent as claimed in claim 10 of formula Ic

    A(X(CH.sub.2).sub.2).sub.3 XA                              (Ic)

or a chelate complex or salt thereof wherein in formula Ic, each Xrepresents a group NA; each A independently represents a hydrogen atomor an alkyl group optionally substituted by a group Y, with the provisothat the two terminal A groups together form a group (CH₂)₂, therebyforming a macrocyclic compound, each Y represents a hydrogen atom, or agroup Z, COZ, SO₃ R⁶, CSZ, PO₂ Z, or B; each group B represents a groupCONR⁷ (NR⁸ ₂), PO(NR⁷ R⁸)₂, SO₂ R⁷, SO₂ NR⁷ R⁸, or NO₂ ; each group Zindependently represents a group OR⁶, SR⁶, or NR⁶ ₂ ; each of the groupsR⁶ independently represents a hydrogen atom, or an alkyl groupoptionally substituted by one or more hydroxy or alkoxy or aryl groups;each of the groups R⁷ and R⁸ independently represents a group R⁶, anaryl group optionally substituted by one or more hydroxy or alkoxygroups, or a lipophilic group; with the provisos that:(1) at least twonon-B ionizable Y groups are present; and (2) at least one Y grouprepresents a non-ionizable group B.
 14. A method of generating enhancedimages of the human or non-human animal body, which method comprisesadministering to said body a diagnostic agent comprising a metal chelateor a salt thereof of a compound of claim
 10. 15. A process for thepreparation of a metal chelate of a compound of formula I as defined inclaim 1, which comprises admixing in a solvent said compound, or a saltor chelate thereof, together with an at least sparingly soluble compoundof said metal.
 16. A process for the preparation of a diagnostic agentwhich comprises admixing a metal chelate of a compound of claim 10, or aphysiologically acceptable salt thereof, together with at least onepharmaceutical or veterinary carrier or excipient.